In recent years, in POCT (Point Of Care Testing), analysis chips (hereinafter refers to as “SPR chips”) using SPR (Surface Plasmon Resonance) have been actively developed. The SPR chip includes a dielectric prism (dielectric medium) and a metal film which is formed over a surface of the dielectric prism and brought into contact with an observation sample.
When excitation light which advances through the inside of the dielectric prism is incident on an interface between the metal film and the dielectric prism while satisfying the total reflection, an evanescent wave leaks out from the interface. Thereby, interference between surface plasmons of the metal film and the evanescent wave is occurred. Further, the surface plasmons and the evanescent wave resonate at an angle at which a resonance angle is set to the incident angle of the excitation light to the interface. Since the resonance angle depends on the dielectric constant of the analysis subject sample, analysis is carried out according to a shift amount of the resonance angle due to the presence/absence of the sample.
Further, as a technique which uses the surface plasmon resonance, SPFS (Surface Plasmon-field enhanced Fluorescence Spectroscopy) is known other than the above-mentioned technique. An analysis chip (hereinafter refers to as “SPFS chips”) using the SPFS is similar to the above-mentioned SPR chip in configuration for exciting the surface plasmons. The SPFS chip differs from the SPR chip in that the former provides an electric field enhancing effect of the evanescent wave caused when the surface plasmons and the evanescent wave resonate, and a florescent substance to the observation sample. In the detection, the above-mentioned enhanced electric field enhances fluorescence from the florescent substance provided to the sample, and by detecting the change, the SPFS chip can realize detection with high sensitively even using the sample having poor concentration, compared to the case using the SPR chip.
As for the analysis chips used in analysis with the above-mentioned surface plasmon resonance, for both the SPR chips and the SPFS chips, it is common in that the dielectric prism provided with the metal film is used as a part of the analysis chip and a specific linearly polarized light (P polarized light) is incident on the dielectric prism as the excitation light to generate the surface plasmon resonance. Further, in recent years, the analysis chips are preferably disposable for every measurement in consideration of efficiency, safety, and the like, of the measurement work, therefore, a dielectric prism materials has been changed from glass to resin which can be used at low cost.
However, by producing the dielectric prism with the resin, heat generated when the prism is formed and internal strain due to stress cause a disorder in a polarization state of the excitation light incident on the prism. For that reason, there have been problems such that a surface plasmon resonance state is unlikely occurred and the detection precision is deteriorated. Especially in the analysis with the SPFS chip, high-sensitive detection can be available as described above. Therefore, higher measurement precision is required in the analysis with the SPFS chip than in the analysis with the SPR chip. That is, it is required a sufficiently high polarization state maintenance rate and a uniform polarization state distribution.
Thereupon, in the case that the dielectric prism is made of the resin, it has been purposed a technique such that, for example, a correcting unit which compensates (corrects) birefringence is provided at a side of a measuring apparatus for performing the SPFS measurement, and the birefringence is corrected by the correcting unit to prevent the disorder of the polarization state (see Patent Document 1 below).